Many improvements have been made on rotary lawn mower blades to facilitate mowing or shredding, such as filaments and plastic discs with serrated peripheries. Some of the improved blades are disclosed in the following patents:
U.S. Pat. No. 4,706,446 discloses a rotary lawn mower having double cutting units, the upper one rotary and the lower one stationary. The two units are concentrically mounted and provided with cutting blades in the adjacent planes of the units such that the blades of the upper rotating unit act as shears against the lower stationary blades.
U.S. Pat. No. 2,917,826 discloses a disc of a lawn trimmer having pocket-like attachments with sharp edges, for edging grass along a side walk or flower bed while the disc is held with its edge perpendicular to the soil.
U.S. Pat. No. 5,056,605 relates to a multipurpose disc cutter having sharp saw teeth around its periphery, pointing upward and downward.
U.S. Pat. No. 4,270,271 discloses a trimmer having two discs concentrically held apart from each other so as to accommodate pivotally mounted and removable blades therebetween.
U.S. Pat. No. 4,295,274 relates to a floor scraper having a disc and a plurality of leaf spring strips having the shape of a Z, each mounted on the disc circumference at one end, the other end of the Z strip being equipped with a flat metal cutter having a front cutting edge facing in the direction of rotation of the disc, the rear side of the cutter being at a slight angle with respect to the plane of the disc.
U.S. Pat. Nos. 4,577,382 and 3,176,455 disclose rotary disc blades or bar blades with saw teeth with different orientations and additional apertures on the disc having one lateral edge as cutting edge so as to increase the cutting rate.
U.S. Pat. No. 5,063,731 relates to brush and tree cutter blades having three spring loaded teeth or slicing blades mounted on the periphery of the hinged blades such that if the teeth hit a hard surface, the teeth will retract within their cages and the blades will deflect upward or downward to avoid damage to the blades and saw teeth.
It is evident that the prior art has not addressed the problem of shredding vegetation into fine pieces during the mowing of lawns so as to speed the decomposition of the cuttings in contact with soil or in a compost pile.